Little rally here with some of my students before tennis clinic - Just working on keeping the ball alive- attempting to keep the ball deep- the two lads down the opposite end are alternating hitting- 1. Excellent warm up for footwork 2. Builds consistency 3. Coach can vary the shots - differing spin - pace- work on students weaknesses. Give this drill a go with a coach or friend next time you are on the court and have 3 players and need to warm up.